The built environment continues to grow rapidly and is currently estimated to account for 30–40% of all Greenhouse Gas (GHG) emissions globally. Continuing on a ‘business as usual’ trajectory will see global annual increases in GHG emissions as a result of considerable urban growth. Some past studies have quantified national GHG emissions associated with the built environment but, to-date, no national framework for GHG emissions accounting of the built environment exists. This study presents a robust methodology for estimating GHG emissions associated with the built environment using Ireland as a case study. Taking a Whole Life Carbon (WLC) perspective it quantifies both operational and embodied emissions. One single method is used for operational emission quantification, for which well-documented data exists. For embodied emissions two methods are applied: 1) Material-based emissions are calculated using the Commodity Accounting Method (CAM) and 2) Sectoral-based emissions are quantified using constructed floor area and other construction-related data (the Sectoral Summation Method – SSM). Reasonable agreement between the methods is observed which enables robust conclusions to be drawn. ∼37% of all Irish GHG emissions are attributed to the built environment while ∼1/3 of these emissions are embodied in the production of the raw materials, the transport of materials and the construction and demolition of buildings and infrastructure.